During a controlled, randomized, double blind study, 30 patients of a neurosurgical intensive care unit were treated with ranitidin and placebo (group 1) or ranitidin and pirenzepin (group 2). No significant difference in the effectivity of both methods was established, presumably due to the small number of cases. The pH values of group 2 lay in the median above 3.5, whereby the difference only became statistically significant after a seven-day period of therapy. In how far the increase of the pH value represents the only factor of a stress ulcer prophylaxis requires further investigation, particularly in connection with pulmonary risks caused by this.